Vishy Anand won the world crown in 2007 and has since defended it by defeating three challengers in matches. The Indian's form has dipped in the past two years and he is currently only No6 in the rankings, yet he will not face a match challenge from the No1, Magnus Carlsen, until at least late 2013.

Contrast that with the plight of Hou Yifan. China's 18-year-old was runner-up for the women's world title in 2008, won it in 2010, then defended it in a match in 2011. She is clearly the all-time female No2 after Hungary's Judit Polgar, who does not play in women's events.

But last week Hou suddenly became an ex-champion in banal circumstances. She wilted in the -17C weather in Siberia which staged the 2012 knockout title contest, developed a heavy cold, and crashed 3-1 in the second round to Poland's Monika Socko, the last two games rapid chess. The world KO reaches its semi-finals today and can be viewed free and live online with computer commentary starting at 9am.

Hou has the right to a 2013 title match, not as ex-champion but because she was first in the women's Grand Prix elite tournament series. Fide, the global chess body, used knockouts for its men's title in 1997-2004, but the system was widely derided for its erratic results. Many lists of historic world champions now exclude the KO winners in favour of Garry Kasparov and Vlad Kramnik who played traditional matches lasting several weeks.

The men's knockout is now downgraded to a World Cup which only qualifies its winner as one of eight title candidates, but the women's championship remains at the mercy of a single off day, as Hou discovered.

Her first round game shows how a top player can outclass an opponent quickly. Black's 9...g5 is inventive but she starts to slip by 12...Bg7 (Bd6 and later Qc7). The real blunder is 16...Rg8? (0-0) when 17 Ngf5! exf5 18 Nxf5 Qe6 19 Nxg7+ Rxg7 20 Rae1 Kd8 21 Bd4 is decisive. After that Black seemed fatalistic and at the finish 25 Qd6! will end it.